A-Alkylation or Alkylidenation of Aminoquinoxalines

The foregoing processes are illustrated in the following examples, not including the 1/4-alkylation of reduced quinoxalines that has been discussed in Section 2.2.2. 

Note The alkylation of nuclear or extranuclear aminoquinoxalines is an unattractive process, and examples are limited. Initial acylation of an aminoquinoxaline is sometimes used to assist subsequent alkylation, and the acyl group can be removed later with ease. 

3-Dimethyl-6-quinoxalinamine with dimethyl methoxymethylenemalonate [Me0CH=C(C02Me)2] gave 6-(2,2-dimethoxycarbonylvinylamino)-2,3-dimethylquinoxaline (141) (MeOH, reflux, 30 min 61%) ° analogs, like 6-(2,2-dicyanovinylamino)-2,3-dimethylquinoxaline (57%) or 6-(2,2-di-acetylvinylamino)-2,3-diphenylquinoxaline (67%), were made similarly. 

7-Nitro-3-(piperazin-l-yl)-2-quinoxalmecarbonitrile (143, R = H) gave 3-(4-ethylpiperazin-l-yl)-7-nitro-2-quinoxalmecarbonitrile (143, R = Et) (EtI, EtOH, reflux, 5 h 50%)7  

Note Such Schiff base formation occurs readily between primary aminoqui-noxqlines and aldehydes, ketones, or their derivatives. 5,6-quinoxalinediamine (144) gave only 6-(p-nitrobenzylideneamino)-5-quinox-alinamine (145) [substrate, MeOH, —5°C, P-O2NC6H4CHOI slowly, 2 h  

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